Clevis and tongue connections are known for connecting a towed vehicle such as a trailer or agricultural implement to a towing vehicle. A problem with such connections is that the drawpin holes in the upper and lower clevis members and the drawpin hole in the tongue extending between them are very often of different sizes.
For example in agriculture, an implement is typically hitched to a tractor drawbar by a clevis and tongue connection. The clevis provides an upper and lower clevis members each defining a drawpin hole, and the tongue defines a drawpin hole and is inserted between the clevis members to align the drawpin holes such that a drawpin can be inserted through them and thereby connect the clevis and tongue. Where the drawpin holes are the same size, a corresponding size of drawpin can be inserted to connect the clevis and tongue in the preferred manner such that there is only minimal movement at the connection.
The clevis may be mounted to the tractor drawbar and the tongue mounted to the implement hitch, or vice versa. Tractors come in a wide variety of sizes, and the tractor drawpin hole is typically sized for a pin of sufficient strength to match the power of the tractor. Implements also come in a wide variety, and similarly have a hitch with a drawpin hole that is sized for a pin of sufficient strength to match the power requirement of the implement. There has been some standardization in the agricultural implement industry, with hitches categorized by size. For example a Category 5 implement hitch will have a 2¾″ (inch) diameter drawpin, a Category 4 will have a 21″ drawpin, and so on.
Since there are typically a limited number of tractors on a farm that are required to tow a wide variety of implements, often the drawpin holes are of different sizes, and a drawpin that fits through the smaller of the holes must be used. The implement and tractor are thus connected by a loose fitting connection that allows significant movement. Control of the implement is thus reduced, and undesirable shock forces are exerted on the drawpin, implement hitch, and tractor drawbar during use, causing excessive wear.
Similarly trailers are commonly attached to a towing vehicle by a pintle hook and ring mechanism. The pintle hook is typically mounted to the towing vehicle, and a ring member is attached to the trailer hitch and drops over the ring member onto the pintle hook to connect the trailer and towing vehicle. The ring member defines a pintle hook aperture into which the pintle hook must fit. Similar to the clevis and tongue mechanism, it is desirable to have the pintle hook aperture fit the pintle hook quite closely.
This problem has been addressed for example in U.S. Pat. No. 5,671,938 to the present inventor Olson. The disclosed implement hitch provides a hitch member defining a drawpin hole that is adjustable by moving a back portion of the hitch member forward and rearward by securing a variety of spacers in the hitch member, or by securing in the hitch member an auxiliary member that defines a smaller drawpin hole. The disclosed hitch requires considerable machining to make, and as well it also requires a significant amount of time to change the size of the drawpin hole.
United States Published Patent Application 2007/0052207 also of the present inventor Olson, discloses implement hitches that provide a hitch member defining a drawpin hole that is adjustable by moving a spacer forward into and rearward out of the rear portion of the drawpin hole. The spacer can be moved incrementally by turning a threaded actuator to accommodate a drawpin of any size.